Modifying the sensitivity of photographic emulsions



April l1, 1939- J. D. KENDALL 2,153,929

MODIFYING TH SENSITIVITY OF PHOTOGRAPHIC EMULSIONS Filed May 25, 1936 3o54- 3s 4a 4s so 54 sa s2 INVENTOR.

. Iuhn D avi d vKIM-L dan.

ATTORNEY Patented Apr. 11, 1939` PATENT orifice MODIFYING THESENSITIVITY PIIOTO- GRAPHIC EMULSIONS 'Y John David Kendall, Ilford,England, assignor to Ilford Limited, Ilford, England, a British companyApplication May 25, 1936, Serial No. 81,782

In Great Britain May 30, 1935 Claims.

in which n is a positive integer, which system may also be representedas -N-(o=o- -c=N I v I I I in which n is yl) or a positive integer.

According to the present invention a method of modifying the sensitivityof a photographic silver halide emulsion comprises treating the emulsionwith a compound which contains the system -N-(-C=C-)-C=Y I I I I (whereY represents S or Se, and n is 0 or a positive integer) and: in whichthe nitrogen atom oi' the above system forms part of a heterocyclicring. f 'I'he present invention also includes 'a photographic silverhalide emulsion in which one or .30 more of the above mentionedcompounds is incorporated.,

Examples of compounds which may be used according to the presentinvention are the a and 'y thiones and selenones of any of the hetero- 3cyclic nitrogen compounds commonly used for the preparation of cyaninedyes, for example unsubstituted and substituted thiazoles, thiazolines,oxazoles, oxazolines, selenazoles, selenazolines, quinolines,indolenines, pyridines, their analogues and homologues including thoseof the benzene and naphthalene series, and alsoA diazoles such aspyrimidine, described in British ?atent No. 425,609.

A convenient method of preparing the thiones 45 and selenones ofcompounds containing a fivemembered heterocyclic nitrogen ring is 'asfollows: The correspondingniercaptan (or selenomercaptan) is alkylated,for example Vwith methyl sulphate in caustic soda solution, to form thethioether (or selenoether) which is then heated l at about. 13G-150 C.for several hours with a molecular proportion of an alkyl sulphate orparatoluenesulphonate to form a quaternary salt; the reaction mixture isthen boiled with a small 55 quantity oi pyridine for about' an hour oruntil complete solution eiected; on dilution the thione (or selenone) isprecipitated and may be purified Yby crystallisation from an alcohol orbenzene or by distillation at low pressures. In many cases the yieldsobtained are almost theoretical when calculated on the quantity .ofthloether (or selenoether) employed.

Many of the compounds which may be employed in accordance with thepresent invention are coloured and absorb portions of the visiblespectrum, in which case they act as so-called optical or coloursensitisers, that is they increase the range of colour sensitivity ofcertain photographic silver halide emulsions. Other compounds possessingthe necessary characteristics are colourless and do not absorb light ofthe visible spectrum, but nevertheless they act as sensitisers andincrease the speed of the emulsion without apparently adding anyadditional colour sensitivity to the emulsion.

In treating the emulsion the substances may be added at any convenientstage during` the preparation of the emulsion before coating it on asupport, or the flnished coated material may be bathed in a solution ofthe substance.

The amount of substance added and the strength ofthe solution forbathing may vary over quite wide limits according to the substances andtypes of emulsions used. In general an addition of the order of 80 ccs.of a $6000 solution oi the substance per unit of l/gditres of emulsionequivalent to 250 gms. of silver nitrate will give useful results, butthe amount added may be as little as 40 ccs. or as much as 400 ccs. oreven more.

In general a 1,4000 solution is used :for bathing but'this may also bevaried in strength over quite wide limits.

' The above methods of treating the emulsions follow the usual knownpractice and in carrying out the present invention it is found thatthese methods are applicable to the cases where com-- pounds areemployed which are coloured or absorb portions of the visible spectrumand increase the range of colour sensitivity of the emulsion. In thecase of the compounds which are .not coloured and do not absorb portionsof the visible spectrum, however, it is found` advantageous toincorporate 'them in the emulsion at an earlier stage during itsproduction, that is they should be added either to the silver nitratesolution or to the alkali halide solution employed in. the preparationof the emulsion.

The following are typical examples of compounds which may be used inaccordance with the present invention and which have colour .sensitisingproperties. N-ethyl-dihydroquinoline2thione extends the sensitivity of asilver chloride gelatin emulsion to-about i 4400 with a maximum at abouti 4100 Nin :Hx N -methyl-dihydroquinoline-i-thione extends thesensitivity of a silver chloride emulsion to about A 4600 with a maximumat about x 4300 CHS N-ethyl-dihydropyridine-Z-thione extends thesensitivity of a silver chloride emulsion to about A 4300 with a maximumeffect at about i 3900 A.

N-methyl-dihydropyridine-Z-thione extends the sensitivity of a silverchloride emulsion to about 7i 4300 with a maximum effect atA about i3900 A.

The sensitivity curves of the above-described emulsions are shown in theaccompanying drawing in which Fig. 1 is a spectrogram of a silverchloride emulsion containing N-ethyldihydroquinoline-2- thione..

Fig. 2 is a spectrogram of a similar emulsion containingN-methyldihydroquinoline-4 -thione.

Fig. 3 is a spectrogram of a. similar emulsion containingN-ethyldihydropyridine-Z-thione.

Fig. 4 is a spectrogram of a similar emulsion containingN-methyldihydripyridine-2thione.

'I'he following examples are given in order to illustrate the use inaccordance with the present invention of compounds which increase thespeed of photographic silver halide emulsions, without having anyapparent eifect on the colour sensitising properties.

Example I A normal unwashed silver chloride emulsion containing a smallproportion, less than 1% together, of silver bromide and silver iodide,was prepared by adding a solution of silver nitrate to a solution ofalkali halide in gelatin and ripening the mixture by maintaining it atF. for fifty minutes. The emulsion was then made up to bulk by theaddition of gelatin solution, iinished in the normal manner, and thencoated on table:

Quantity of Relative solution exposure Fog added time Cubic centimetersNone 850 0.00

Another series of experiments was carried out in which the solution ofthe compound was added to the silver nitrate solution before the silvernitrate was added to the alkali halide; the figures for this series ofexperiments are given in the following table, from which it will be seenthat the variation in procedure does not make any material alteration inthe result:

Quantity of Relative solution exposure Fog added time Gubc centimetersNone 850 0. 00 100 470 00 200 220 00 400 z 01 In the above experimentsthe data relating to emulsion speeds was derived from the characteristiccurve of the emulsion obtained in following manner: A strip of papercoated with the emulsion was exposed under a normal step- Wedge of knowncharacteristics at a known distance from a calibrated light source inthe form of a half-watt lamp of known intensity. The strip was thenprocessed under standard conditions, i. e. developed for one minute at65 F. in a standard metol hydroquinone developer as normally used forgaslight papers, fixed, and then washed, to produce an image comprisinga series of patches varying in density inversely in accordance with thedensities of the corresponding patches of the step-wedge. These patchesof graded density were then lexamined in a standard reflectiondensitometer and their densities so determined were. plotted against thelogarithms of the exposures employed to produce them so giving thecharacteristic curve.

'I'he logarithms of the corresponding exposures can be easily obtainedfrom the known intensity of the light source, the distance at which theexposure was made and the transmission densities of the respectivestrips of the neutral step-wedge employed.

From this characteristic curve the relative exposure time is obtained byinterpolation and is expressed as the number of candle meter secondslexposure to light.

Similar series of experimentsvwere carried out .y usingN-ethyl-dihydrobenzthiazole-1-thione in with similar results,

veo

N-ethyl-dihydrobenzoxazole 1 'thione except that the speed increase wasnot quite so large.

Similar results were also obtained by using N-methyl-dihydrobenzthiazole-l-thione, N-methyldihydrobenzoxazole- 1-thione, N methyl- 5:6 benzdihydrobenzthiazole-1-thione and N-methyl-4:5dimethyldihydrobenzoxazole- 1 thione, with the the exception that theincrease in speed was not quite so great.

Example II The experiments described below illustrate the effect of thevaddition of compounds such as described in Example I to an emulsion oflow initial sensitivity prepared from inert gelatin.

In this case a normal iodobromide emulsion was made up by adding asolution of silver nitrate to a solution of ammonium bromide, potas siumiodide and a gelatin known to yield emulsions of a slow type; themixture was ripened by maintaining it at a temperature of F. for twentyminutes.' Further quantities of silver nitrate and .gelatin of the samekind were then added and the emulsion was set, shredded,

washed, and then digested by maintaining at a temperature of F. forilfty minutes.

The emulsion was then cooled and coated upon glass plates.

A similar batch of emulsion was prepared with the addition of a quantityof a dilute solution of `N ethyldihydrobenzoxazole 1 thione. Thequantity was equivalent to 80 ccs. oi.' solution per unit of 61/2 litresof emulsion equivalent to 250 gms. of silver nitrate, the solution beingadded partly to the gelatin solution of the alkali halides and partly tothe bulk gelatin added after the ripening stage, the quantities added toeach being proportional to the quantity of gelatin added at each stage,the emulsion being further treated as above (i. e. washed,digested,.etc.)

Strips of these plates were then exposed under a neutral .step-wedge ata known distance from a light source of known characteristics and thenIdeveloped for eight minutes at 65 F. in a normal metol-hydroquinonedeveloper as commonly employed for this type of emulsion, iixed, washedand dried and-tested as follows: The characteristic curves were obtainedby measuring the den' sities of the'graded patches of the test image ina standard transmission densitometer and by plotting them ragainst thelogarithms of the exposures producing them, which are obtained directlyfrom the known characteristics, that is the intensity of the lightsource, the distance at which the exposure was made and they knowntransmission density of the corresponding patches of the step-wedge.

From these curves two speed iigures were obtained, one C as thereciprocal of the anti-logarithm of the exposure at which the curveshowed a density of 0.1 above the minimum fog density.

and T. S. as the reciprocal of the anti-logarithm of the-.exposure ofthe point on the curve at which a tangent to the curve makes an angletan-0:02 with the abscissa.

As before the fog values were obtained as the density measured in thesame densitometer oi a portion of the plate unexposed to light anddeveloped, iixed and washed and dried under the same conditions.

The foilowing results were obtained:

Quantity of Speed Speed solution added Fog C TS Cubic centimeters None04 50 74 80 06 52 85 A further experiment wasl carried out in a isimilar manner using a different gelatin and adding the compound to theiirst addition of silver nitrate solution, and otherwise proceeding asbefore.

Results obtained from this experiment were as Both results show anincrease in speed on the addition of the 80 ccs. of solution with aslight increase in fog.

Similar series of experiments were carried4 out with emulsionscontaining varying quantities o f N-ethyl-dihydro-benzoxazole-1thioneand digested for varying times. The results showed that with increasingquantities of the compound added the vsame emulsion speeds were obtainedin shorter digestion times.

I claim:

1. A photographic silver halide emulsion Vof modiiied sensitivity inwhich is incorporated in sensitizing amountsN-ethyl-dihydrobenzoxazolel-thione.

2. A photographic silver halide emulsion of modified sensitivity inwhich is incorporated in sensitizing amountsN-ethyl-dihydrobenzthiazolel-thione.

3. A photographic silver halide emulsion of modified sensitivity inwhich is incorporated in sensitizing amounts N-ethyl-dihydroquinoline-2-thione.

4. A photographic `silver halide emulsion containing in sensitizingamounts a mononuclear heterocyclic mono-nitrogen compound selected fromthe group consisting of a thiones and selenones of the N-hydrocarbonsubstituted thiazoles,

benzoxazoles, naphthaoxazoles, oxazolines, selenazoles, benzselenazoles, naphthaselenazoles, selenazolines, indolenines,pyridines, quinolines, and y thiones and selenones of N-alkylsubstituted pyridines, quinolines and naphthaquino-- lines.

6. A photographic silver halide emulsion containing in sensitizingamounts a mono-nuclear heterocyclic mono-nitrogen compound selected fromthe group consisting of a thiones and selenones of the N-hydrocarbonsubstituted oxazoles selected from the group consisting of oxazoles,benzoxazoles and naphthaoxazoles.

7. A photographic silver halide emulsion containing in sensltizingamounts of a mono-nuclear heterocyclic mono-nitrogen compound selectedfrom the group consisting of a thiones and sele- .nones of the N-alkylsubstituted oxazoles selected v from the group consisting of oXazoles,benzoxaazoles taken from the group consisting of thi azoles,benzthiazoles and naphthathiazoles.

10. A photographic silver halide emulsion con-l taining in sensitizingamounts. a mononuclear heterocyclic mono-nitrogen compound selected fromthe group consisting of the a thiones and Patent No 2,155-, 929.

JOHN DAVID KENDALL.

selenones of the N-alkyl substituted thiazoles taken from the groupconsisting of thiazoles. benzthiazoles and naphthathiazoles.

11. A photographic silver halide emulsion containing in sensitizingamounts a mononuclear heterocyclic mononitrogen compound selected fromthe group consisting of the a thiones and selenones of the N-lower alkylsubstituted thiazoles'taken from the group consisting of thiazoles,benzthiazoles and naphthathiazoles.

12. A photographic silver halide emulsion containing in sensitizingamounts a mono-nuclear heterocyclic nitrogen ycompound selected from thegroup consisting of a thiones and selenones of N-hydrocarbon substitutedcompounds selected from the group consisting of pyridine, quinolines andnaphthaquinoline.

y 13. A photographic silver halide emulsion in sensitizing amounts, amono-nuclear heterocyclic nitrogen compound selected from the groupconsisting of a thiones of N -hydrocarbon substituted compounds selectedfrom the group consisting of pyridine, quinoline and naphthaquinoline.

14. A photographic silver halide emulsion in sensitizing amounts, amono-nuclear heterocyclic nitrogen compound selected from the groupconsisting of a thiones and selenones of N-alkyl substituted compoundsselected from the group consisting of pyridine, quinoline andnaphthaquinoline.

15. A photographic silver halide emulsion in sensitizing amounts, amono-nuclear heterocyclic nitrogen compound selected from the groupconsisting of a thiones and selenones of N-lower alkyl substitutedcompounds selected from. the

group consisting of pyridine, quinoline and naph,

thaquinoline.

JOHN DAVID KENDALL.

CERTIFI GATE OF CORRECTION April 11, 1959.

It is hereby certified that error appears in the printed specificationof the above ninnbered patent requiring correction as follows: Page. l5,first column, line 22, for "the the read the; same'page, second column,line 67,

claim Ly., for "thions" read thiones;`

page li, first column, line l5, claim 7, strike out the word "of"; andthat the said Letters'latent should be read with this correction thereinthat the same may conform to the record of the case in the PatentOffice.

Signed and sealed this 6th day of.

(Seal) June, A. D. 1959.

Henry Van Arsdale Acting Commissioner of Patents.

